MBE is a method for depositing thin crystalline films through the interaction of atomic or molecular beams with a heated crystalline substrate in ultra-high vacuum. It was invented in the 1960s and allows for very low growth rates around 3000nm per hour, enabling the deposition of pure monocrystalline layers. Key components of an MBE system include effusion cells that evaporate source materials, a substrate manipulator for heating and rotating the substrate, and various analytical tools like RHEED and RGA for characterization during growth. MBE provides precise control over film composition and allows separate evaporation of different materials, making it useful for applications like semiconductor devices.

1. MOLECULAR BEAM
EPITAXY
BY
DEEPAK SURESH BABU
MATERIALS SCIENCE AND TECHNOLOGY
M150356ME

2. Introduction
Invented in the late 1960s at Bell Telephone
Laboratory by J. R. Arthur and Alfred .Y .Cho
MBE is a method of depositing monocrystalline thin film
over a substrate
What does beam mean?
 Means that evaporated atoms do not interact with each
other or vacuum chamber gases until they reach the
wafer
Deposition rate is 3000nm per hour

3. What is Epitaxy?
Deposition and growth of monocrystalline layer over
substrate
Epitaxy Types
Homoepitaxy: Substrate & material
are of same kind .(Si-Si)
Heteroepitaxy: Substrate & material
are of different kinds. (Ga-As)

4. MOLECULAR BEAM EPITAXY

5. Working Principle
Epitaxial growth
Due to the interaction of molecular or atomic beams on
a surface of a heated crystalline substrate.
The solid source materials sublimate
They provide an angular distribution of atoms or
molecules in a beam.
The substrate is heated to the necessary temperature.
The gaseous elements then condense on the wafer
where they may react with each other.

6. Basic Components
Vacuum Chamber
Stainless steel chamber
Ultra High Vacuum( 10−8Torr)
Connected to preparation chamber
Preparation chamber is used for degassing substrate

7. Pumping System
Must be able to reduce residual impurities to minimum
Partial pressure of order 10−8
to 10−12
Torr
Ion pumps and Cryogenic pumps used
Liquid N2 Cryopanels
Surrounds internally both main chamber wall and source
flange
Cools chamber and substrate
Liquid nitrogen at temperature of 77 Kelvin

8. Effusion Cells
Also called Knudsen cells
Thermal evaporation source
Major parts
Crucible
Filament
Heat shielding
Thermocouple
Shutter

9. Crucible
Pyrolotic boron nitride
Can withstand a temperature of 1300ºC
Filament
Made up of Tantalum(Ta)
Computer controlled shutter which regulates flux
Shutters operated faster than growth rate(0.1s)
Shutters are made up molybdenum or tantalum

10. Substrate Manipulator
Capable of continous azimutal rotation
Substrate holder is made of Molybdenum
Heater is fixed behind the substrate holder for uniform
heating of substrate
Ionisation gauge is fixed opposite substrate holder to
monitor beam intensity

11. RHEED
Reflection High Energy X ray Diffraction
Used to characterize the surface of crystalline material
To analyze the grain growth
This technique employs a high energy (up to 20 KeV)
electron beam, directed on the sample surface
The diffraction pattern is imaged on a symmetrically
placed fluorescent screen

12. Residual Gas Analyzer (RGA)
Used to quantify ion content in the chamber
Quantify the atoms that have not incorporated in the
epitaxial film.
Additionally RGA is used to detect the impurity in the
chamber and leakage in the vacuum system.

13. Benefits
Highest acheivable pure layers are formed
Low growth rate of order 3000 nm per hour giving
monocrystalline layer
Controllable thermal evaporation
Separate evaporation for each material

14. Limitations
Very expensive about 106
$ per MBE chamber
Very complicated system
Ultra high vaccum required

15. Applications
For manufacturing of
Semiconductor devices
Transistors in cell phones and Wifi
Microelectronic devices
Super lattices

16. THANK YOU